Highly fluorinated alternating copolymers possessing high glass transition temperature and cross-linking capabilities under extreme UV radiation

Abstract

In this presentation, we show our efforts toward the discovery of extreme UV (EUV) resists based on the radical reactions that highly fluorinated molecular units undergo. Recently, we reported that small molecules equipped with perfluoroalkyl ether (PFAE) chains or fluoroarene units show solubility change under high-energy electron beam (e-beam) or EUV light via intermolecular chemical network formation. Although this non-chemical amplification-type imaging mechanism worked without the help of any catalytic species, its low sensitivity characteristics had to be improved for practical use. A solution was sought in polymeric resist platforms, particularly those possessing a uniform composition and high enough glass transition temperature (Tg). A perfluoroalkyl moiety was introduced to maleimide (Mi) to give RFMi, which could then be copolymerized in an alternating manner with styrene (P1) and a styrenic derivative containing a Sn atom (P2) or acid-labile protective group (P3). By using a reversible deactivation radical polymerization method, the copolymers could have narrow molecular weight distributions (polydispersity index (PDI) < 1.5) along with their uniform monomer compositions. Thanks to the rigid backbone structure enabled by the maleimide units, the perfluoroalkylated copolymers could be characterized by high Tgs over 100‡C. When lithographic patterning tests were performed under EUV exposure conditions, the thin films of all the alternating copolymers could be tailored down to the 30-nm size, and in particular, the one with Sn atoms (P2) made patterns with 22 mJ/cm2. These results demonstrate the useful nature of the imaging chemistry that highly fluorinated molecular units enable under high energy radiation.